The invention relates to a method for operating a wiper drive having a motor, a computer program product with program code which is stored on a non-transient machine-readable carrier, and a control device for a wiper drive. In particular, the invention relates here to the load-dependency of the motor torque during wiping. Embodiments of the invention also relate to a windshield wiper device and to a method for performing closed-loop and/or open-loop control of a windshield wiper device, in particular for a motor vehicle having an electronically actuated wiper drive motor.
Numerous methods for controlling wiper drives (WSAs) are known. For example, DE 101 44 985 describes a drive which drives a wiper via a wiper shaft and a torque which is dependent on the position of the gear mechanism. In this context, a controller is used in such a way that the torque which is output by a motor is determined at every point in time by taking into account the transmission ratio. In these methods, the wiper motor is actuated in each case in such a way that the position of the wiper blade on the windshield always moves on a setpoint trajectory. In other methods, in the critical regions of the windshield wiper device the wiper motor is reduced in terms of the maximum torque which it can output by reducing the voltage supply via an actuator unit. In windshield wiper devices with direct drive of the wiper levers via the drive motor without an intermediately connected linkage, the drive is powered down when a maximum permissible torque for the permanent operation of the gear mechanism is reached, in order to protect the gear mechanism.
In wiper drives (WSAs), the components are loaded during operation by forces. In this context, in the case of wiper drives such as are used, for example, in motor vehicles for windshield wipers, these forces increase, in particular in the case of snow load, wind load or in the case of blocking of the wiper. In particular, very large loads can occur in the latter case of blocking, in particular in the case of rigid systems.
Typically, in wiper systems with direct wiper drives, drives are used with reversing electric motors in which the motor for generating the to and fro movement of the wiper changes the rotational direction. In this context, the wiper blade changes the direction of movement in a lower or upper turning position. The use of such reversing motors also permits an extended parked position (EPS).
A limited voltage and therefore a limited motor torque for limiting the load can be fed by pulse width modulation (PWM) to an electric motor contained in a wiper drive, as a protective function against damage or destruction. Limiting here serves to protect against damage and to promote compliance with specifications in order to ensure the service life of the components. However, there are operating modes in which limiting brings about blocking of the wiper system, which at least restricts the comfort from the point of view of a vehicle driver.